Recognizing ligand binding sites

[Jessica Hu 3L]

Hi! how can we tell how many sites a ligand will bond to (for example the difference between a monodentate and a bidentate?) And how much will we need to know for this final exam?

[StephanieGrigorian2J]

A monodentate will bind at only one site (donating one electron pair as it binds) while a bidentate will bind at two sites (donating two electron pairs as it binds).
tridentate = 3 sites
hexadentate = 6 sites
Keep in mind that bidentate, tridentate, and hexadentate ligands are also chelating ligands, meaning they can form a ring like structure.

[Khoa Vu 3l]

You can tell how many sites a ligand can bind to by first seeing how many available lone pairs on different atoms can be donated. Only one lone can be donated per atom due to its orientation locking into place after it donates its lone pair. However, chelating ligands use spacer atoms or carbons with sigma bonds between atoms that have donatable lone pairs. This allows the molecule to rotate the orientation of the atoms with donatable lone pairs to face the central atom to donate multiple its lone pairs. For example, en, or C2H4(NH2)2, has two nitrogens that can donate a lone pair, making it bidentate, but it can only donate those two lone pairs thanks to the spacer carbons with sigma bonds allowing the nitrogens to rotate themselves towards the central atom to donate their lone pairs.

[Nancy Yao]

1 lone pair to form 1 bond: monodentate
2 lone pairs to form 2 bonds: bidentate ligand
3 lone pairs to form 3 bonds: tridentate ligand
6 lone pairs to form 6 bonds: hexadentate ligand

[Veronica Macias 3K]

I was struggling with this, but these posts are really helpful!

[Grace_Remphrey_2J]

As explained in the posts above, the number of lone pairs on an atom that can be donated will affect the number of possible ligand binding sites.